Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $220.83   11.340%   $245.8721   $245.87   $245.85   $245.90  
  Purchase #2 $72.36   4.622%   $75.7045   $75.70   $75.70   $75.70  
  Purchase #3 $114.41   10.110%   $125.9769   $125.98   $126.00   $126.00  
  Purchase #4 $41.26   3.803%   $42.8291   $42.83   $42.85   $42.80  
  Purchase #5 $167.71   13.856%   $190.9479   $190.95   $190.95   $190.90  
  Purchase #6 $128.98   9.850%   $141.6845   $141.68   $141.70   $141.70  
  Purchase #7 $57.75   3.823%   $59.9578   $59.96   $59.95   $60.00  
  7 purchase totals = $803.30       $882.9728   $882.97   $883.00   $883.00